Method for producing alloy steel wool



United States Pate 3,234,056 Patented Feb. 8, 1966 3,234,056 METHOD FOR .PRUDUCING ALLOY STEEL WOOL Paul Kraft and Josef Schliirner, Reinb ek, Bezirk Ham- 'burg, Germany, assignors, by mesne assignments, to Wurttrnberg'ische Metallwarenfabrik, Geislingen an der Steige, Germany i No Drawing. Filed. Oct. 15, 1962, Ser. No. 230,737 7 Claims. (Cl. 14816) The present invention relates to a metallic corrosionresistant andoxidation-resistant material and articles made therefrom, and relates especially to metallic materials and Shaped articles which are of porous character. The said material is particularly suitable for use for filter and machine parts. The present invention relates also to a method for producing the new material.

Metallic porous materials are known and have vfound use in the most varied of industrial applications. These materials ar-e usually manufactured by powder metallurgy methods. Materials which are based upon iron, copper or bronz'e cannot be considered to be corrosion-resistant. In order to obtain corrosion-resistant materials, a powder of aVZgImater iaI has been used. Materials made from VZd powder likewise do not fulfill the usual requirements as to corrosion-resistance, because rustless steels are only resistant to reactive gases, vapors and liquids, if they have completely smooth and polished surfaces, no corners orcre'vic'es are present in which residues can collect and the texture is completely homogeneous, in order to prevent the formation of local elements.

Known surface treatments with corrosion-resistant metals, for example, a diffusion treatment with chromium (chromising process) of, for example, workpieces formed by pressing non-corrosion-resistant metals in powder form,do not give the desired result. A very good corrosion-resistant surface layer can be applied to such workpieces, but this known method does not succeed in making corrosion-resistant the central zone of a workpiece or shaped article, which in many cases is necessary, particularly if such a workpiece is subsequently mechani cally treatedorworkedfi It is an object of the invention to provide a metallic material avoiding the previous disadvantages. In carrying out the above object, it is another object to provide a material consisting of metal threads, particularly steel wool fibres, plated or coated with alloying constituents imparting temperature, corrosion and/ or oxidation resistance to the basic metal of the threads, and then homogenised by diffusion annealing.

Another object of the invention is to provide a porous metallic material consisting of skeleton-like felted metal threads, particularly steel wool fibres, which form a network, which fibres or threads have first been gas phase plated with chromium impartingternperature, corrosion and/ or oxidation resistance to the basic metal of said fibres or -t-hr'eads, and then have been homogenised by diffusion annealing.

A further object of the invention is to provide a porous metallicmaterial for subsequent use as filter or machine parts, the material consisting of skeleton-like felted and pressed steel wool fibres which form a network, which steel wool fibres are homogeneously alloyed with chromium, and whereby the chromium content of the alloy may amount up to 40 percent by weight.

Yet another object of the invention is to provide a porous metallic material consisting of steel wool fibres in the form of a network, which steel wool fibres are homogeneously alloyed with aluminum and wherein the aluminum content of the alloy may amount up to 10 percent by weight.

Yet another object of the invention is to provide a porous metallic material consisting of steel wool fibres in the form of a network, which steel wool fibres are homogeneously alloyed with nickel, and wherein the nickel content of the alloy may amount up to 15 percent by Weight.

Specifically the invention is directed to the method of producing the new material which consists in subjecting metal threads to a surface treatment of plating or coating with at least one metal which forms an alloy with the basic metal of the threads imparting temperature, corrosion and/ or oxidation resistance, and then homogenising the material by diffusion annealing at high temperatures. The material may be finally compressed into shaped articles, but the metal threads can also be pressed and shaped in the untreated state (green state) and plated and homogenised as previously described as shaped articles.

' Further objects and advantages of the present invention will be apparent from the following description.

The invention comprises using, as the base material, metal wool, particularly steel wool, and the separate threads are improved by an otherwise known process in such a way that not only is the surface altered, as is the case with the known method, but by subsequent annealing and homogenising, the shaped article as a whole receives the desired properties, even throughout its inner central regions.

It is possible firstly to shape the metal threads into plates or discs or other forms, if required, by sintering, before the surface plating with the improving or hardening metal is applied. In the shaping, the metal threads interpenetrate, so that an open network is produced, which nevertheless is quite resistant to deformation and has a certain mechanical strength, although it can contain up to of voids. In applying coatings, deposition occurs not only on the outer surfaces of the metal thread article, but also the, for example, metal vapors, solutions, melts or powder mixtures containing the alloying constituent-s penetrate through the whole network so that a layer is deposited on the separate metal threads throughout the whole of the internal region. In the subsequent diffusion annealing at suitable temperatures, the alloying metal diffuses from the applied layer to establish an equilibrium in the separate threads and a completely homogeneously alloyed metal thread structure is formed which is suitable for preparation of completely corrosion-resistant articles.

All known methods can be employed for carrying out the metal plating step, such as, for example, metal vapor treatment, immersion in metal melts, immersion in alloying agent powders, immersion in salt baths (electroless metal deposition) and also immersion in aqueous salt solutions with subsequent reduction at high temperatures e. g. under hydrogen.

The diffusion annealing accompanying the plating is carried out at such a temperature and for such a duration that the separate metal threads become completely coated with for example, a high chromium content material, and finally become homogeneously alloyed. As a rule, temperatures of about or above 1,000 C. are used. Sufficient homogenising is usually obtained after up to three hours. According to certain circumstances, in which the velocity ofdiffusion of the plating layer is very slight, for example with nickel on steel wool, longer times of up to ten to twenty hours, for example are necessary.

Gas-phase plating of steel wool fibres with chromium is preferably carried out at temperatures of 1000" to 1100 C. for two to three hours and annealing advantageously proceeds for 0.5 to 3 hours at 1100 to 1400 C. The diffusion and annealing treatment can take place in one stage, preferably at 1100to 1200" C. for one to three hours, together with the gas-phase plating step.

Chromium is preferred in many cases as the metal used in gas-phase plating. Other metals, such as nickel or aluminum, can also be used in the process of the invention.

In the manufacture according to the inventionof a material using, for example, steel-fibres and chromium as the improving agent, a chromium content in the steel wool of about 40% is obtained. This provides an'assurance of a satisfactory oxidation and corrosion resistance of the materialin subsequent mechanical treatment. virtually unaltered by this treatment The ductility and elasticity of the metal fibers likewise remain substantially the same. These properties are of great importance 7 for the later working and use of these materials.-

The material used according to the invention as the basic material is advantageously obtained by cutting from metal wire or strip and is used in the form of fibres rangin-g n size from one thousandth toseveral tenths of a milhmetre in width, one thousandth to several millimeters in breadth and up to several metres in length. Steelwool fibres which undergo substantially no alteration of tor-m on being chromised, for instance, are particularly suitable.

The material according to the invention can be Incchanically worked with comparatively little wastage be- The surface character of the metal fibres remains 4 drogen chloride were introduced which,'by reaction with the chromium pieces. and gth'e steel. wool, efiected the chromising process. The diffusion and annealing treatment was carried out in one stage for two hours at temperatures between 1150 and 1180 C. .Aftercooling, the.

original appearance otthe material was substantially unaltered. A porous steel=wool yarn only; slightly altered in external volumewas produced which had consider-able corrosion-resistance and was capable of :being usedfas a constructional material or a variety of purposes.

Example 2 A steel wool hank about 1 m.- long with an average thread cross-section of 0.05 x 0.5 mm. was-immersed in cause or" its good ductility and elasticity and thus always retains its corrosion-resistance. For example, .a steel wool material homogenised and diffusion-treated with chromium was wound on a roller, which has an all-glee iron frame, and after being covered with a linen or felt cloth, is used in ironing machines and' wringing apparatus. Hot water vapor is led to the inside of the roller and the roller covering must therefore be absolutely corrosion,

resistant and also permeable to steam. These require-v men-ts are .met in an ideal way. by the material according to the invention. Similar roller arrangements are required in the ceramic industry for the dewatering of slip. materials. The roller dips into the slip at the underside. and takes up a thin layer of it; Inside the roller. filter,

a vacuum is produced, whereby the excess water is filteredofi. In this particular kind of use, stringent conditions are imposed as regards resistance. The high porosity. of;

e.g. chromised steel wool produced according to the" process of the invent-ion is very' well suited to the: uses;

of such a device made from the material according to the invention.

Together with such machine parts filters themselves;

can advantageously be manufactured with thematerial according to the invention. Such filters are especially well suited for dust filtering in sO -conta-inin'g, moist hot atmospheres.

The material according to the invention is particularly. suitably, because of its high oxidation and COI'I'QSIOl'l-tl'fin sistance and low specific gravity with high porosity, for

.a suspension consisting ofmethyl alcohol andxl0 parts of a steel. containing about 610% of alumin um,

This material is very oxidation-resistant and can-be made into a high temperature filterwhich ,can be used in an oxidizing atmosphere.

Example 3 s A steel 'w'ooliy-arn corresponding 1 to Example .2 was immersed in an'aqueous saturated nickel nitrate solu;

tion. Because of the extensive capillary action, the "steel wool materialtook up the solution completely. By careful drying at *120" C. the solution was evaporated'and,5

on the surface of the steel. wool-fibres, a thin saltcrust remained. The steel wool material was then subjected to ditfusion annealing at 1200- to 1400 C; By heating in the temperature range of 800 to 1000 C. the nickel nitrate was first reduced to metallic nickel and, in the further annealing treatment, this nickel: was'diffus'dinto thesteel wool. Because of the low'dififusion velocity of nickel, the annealing process wasv carried out for 10 to 20 hours. After the annealing treatment, a thread was ob} tained which consisted of a high nickel content steel containing about 15% nickel.

By means of compressing in :a steel matrix comprising about 5 tons per square cm., a. pore volummof about 80% was reduced to only 10%. Such alpartis ideally suitedas a turbine blade for swea cooling.,,

If necessary the shaped article of steel wall can be im mersed, before being compressed, in a ceramic slip and,

the manufacture of turbine. blades for so-called sweat.

cooling at high temperatures- In the following, various embodiments of the method of the invention are describedin detail. These embodiments, in which temperatures are given on the centigrade scale," serve as illustrations, only, and are not intended to limit the present invention in scope.

Example 1 Steel wool hanks consisting of numerous separate threads which were obtained from a special steel Wire of" the following analysis, 0.13% C, 1.06% Mn, 0.042% P,

0.009% S, 0.05% Cr and traces of Si by cutting, were laid out in parallel form and introduced into an upright chromising retort. Chromium and ceramic pieces were packed into the retort so that no pressure or tension could and hydrogen'as a protective gas was introduced through the closed retort Simultaneously,-small amounts of hy-.

a be exerted on the steel wool yarn. A mixture of nitrogen after drying, can then he pressed as has been described. In this case, sintering at 1400 to.1500. C. is necessary, in order'to give the part the desiredstrength. Such apart is most suitable for use in combustion turbines.

While the embodiments of the present. invention as herein disclosed iconstitute preferred examples,-,it is to 'be understood that. other: compositions and forms might be adopted.

We claim: 1. A method of producing metal alloys, comprising ap plying toa multiplicity of steel fibers oriented. at random as a ibodylof steel wool a coating of -a metal selected from. the class consistingof chromium, aluminum and nickel with the surface of the fibers coated with the coat-. ing metal throughout the. body of steel. wool,- and ma-in-.

taining the body of steel wool at elevated temperature to difi-use the coating metal through the thickness of each fiber until the concentrationof the coating metal is su-bi stantially uniform throughout. the thickness of each fiber.

2.1 A method as claimed in claim 1, in which the coating metal is chromium.

3; A method as claimed in claim 1, in which't he coating metal is aluminium.

4. A method as claimed in claim 1, in which the coating metal is nickel.

5. A method as claimed in claim 1, and compressing the body of steel W001 to a desired shape prior to said coating step.

6. A method as claimed in claim 5, and sintering the body of steel wool to Weld the fibers together at their points of contact, said sintening step being penfonmed after said compression step and before said coating step.

7. A method as claimed in claim 1, and compressing the body of steel Wool to a desired shape after said diffusion step.

References Cited by the Examiner UNITED STATES PATENTS 1,243,654 10/1917 Clark 11750 6 Meeker et a1. 148-16 Brennon 117l07 Kohr ing 117l07 Samuel 117107.2

Samuel 14816 Drummond 117107.2 Becker et al 117107.2

Shepard 117l07 Martenson et a1. 148-16 Mongan 14812.1

DAVID L. RECK, Primary Examiner. 

1. A METHOD OF PRODUCING METAL ALLOYS, COMPRISING APPLYING TO A MILTIPLICITY OF STEEL FIBERS ORIENTED AT RANDOM AS A BODY OF STEEL WOOL A COATING OF A METAL SELECTED FROM THE CLASS CONSISTING OF CHROMIUM, ALUMINUM AND NICKEL WITH THE SURFACE OF THE FIBERS COATED WITH THE COATING METAL THROUGHOUT THE BODY OF STEEL WOOL, AND MAINTAINING THE BODY OF STEEL WOOL AT ELEVATED TEMPERATURE TO DIFFUSE THE COATING METAL THROUGH THE THICKNESS OF EACH FIBER UNTIL THE CONCENTRATION OF THE COATING METAL IS SUBSTANTIALLY UNIFORM THROUGHOUT THE THICKNESS OF EACH FIBER. 